The present invention relates to a machine for use in making concrete pipe. In particular, the invention relates to a seal for containing the slurry which is created during vibration of concrete mixes used to make concrete pipes. The seal of the present invention allows for improved quality in the manufacture of concrete pipe, in both dry cast and wet cast processes.
The most common method of forming concrete pipe entails the use of vertically oriented cylindrical forms. The form, or outer jacket (sometimes referred to as a mold), is used to form the outside surface of the concrete pipe, while a core is used to form the inside surface of the pipe. Ring-like forming equipment is used to create male and female connections at the opposite ends of the concrete pipe. A pallet is used to form the lower female end, while a cap is used to form the upper male end. Reinforcing bars, commonly referred to as a cage, may be used in some cases to form a pipe of increased strength.
Generally, the first step in the concrete pipe manufacturing process is to form a cage and place it onto a pallet. The pallet and cage are placed over a core. Lifting feet extend outwardly from the bottom of the core to engage the underside of the pallet so that when the core is lifted the core, cage and pallet are raised as a unit. That assembly is then lowered into place within a form. The assembly is then ready for the placement of concrete between the form and the core around the bars comprising the cage. To ensure the complete flow of concrete and to avoid the formation of voids, vibrating equipment is generally used to enhance the flow of the concrete mix. Such vibration causes the concrete mix to consolidate or densify. Vibration of the concrete mix results in the formation of a slurry, i.e. a combination of water, cement paste and fine sand in suspension. The slurry, being generally a liquid-like material, tends to flow through available cracks or opening. Vibration and the resulting slurry are present both in wet and dry casting processes.
In dry casting, once the form is filled with concrete and the cap has been placed around the top to form the male end of the pipe, the pipe is separated from the form. The separation is accomplished by lifting the core and pipe out of the form. The pipe and core are then separated by retracting the core feet and withdrawing the core from the pipe.
In wet casting, once the form is filled with concrete and the cap has been placed around the top to form the male end of the pipe, the pipe, form, core, cap and pallet are left for the concrete to cure. Once the concrete has cured sufficiently, the pipe is then separated from the mold, core, cap and pallet.
The processes explained above have been used for many years and are generally accepted and effective methods of forming concrete pipe. However, because of the relative vertical movement required to separate the various components of the manufacturing system, the formation of an effective seal between the core and the pallet, and between the pallet and the form has been a significant problem. Compression seals are used in some cases. However, such seals have generally been used in connection with ledges, such that generally horizontal opposing surfaces are used to compress an elastomeric material. Such a sealing arrangement relies on the gravitational force created by various components of the system, making the design of an effective seal largely dependent on factors which cannot be varied, i.e. the weight of the respective components.
The use of ledges to support the elastomeric material comprising the compression seal creates problems of interference when separating the components of the system is required. A ledge-type support for a seal may only be used at one of the two sealing locations, i.e. the inner or the outer edge of the pallet.
In addition, the ledges used to support compression seals, and the upwardly facing grooves in which the seals rest, provide a place for significant buildup of excess slurry. The excess slurry hardens under the compression seals and creates an uneven base upon which the seal rests, unless the upwardly facing grooves are cleaned after each use. As a result of the difficulty in obtaining an effective seal at the lower regions of a concrete pipe forming assembly, significant losses of slurry can occur. Substantial losses of slurry can result in weak sections within the resulting concrete pipe which may, in addition, have poor appearance.
Therefore, it is an object of the present invention to provide a concrete pipe making system in which loss of slurry is substantially reduced or eliminated.
Another object of the present invention is to provide a concrete pipe making system in which an effective and reliable seal is capable of being formed at the interfaces between the pallet and the core, and between the pallet and the form.
Still another object of the invention is to provide a method of forming concrete pipe which is substantially free of structurally weakened areas which are the result of excessive loss of slurry.
Still another object of the invention is to provide a method of forming concrete pipe having uniform appearance.
These and other objects of the invention may be achieved with a concrete pipe making system which utilizes laterally expandable seals which close the gap between the pallet and the core, and between the pallet and the form of a pipe making apparatus. The laterally expandable seals are comprised of two annular hollow tubes made of a resilient elastomeric material. These annual sealing elements are housed within grooves formed on the lower portions of the core and form. The hollow sealing components are expanded by the insertion of fluid (gas or liquid) to cause expansion of the sealing component out of the groove into engagement with vertical inner and outer surfaces of the pallet. Once the sealing components have been pressurized, vibration of the concrete pipe forming apparatus can proceed without danger of loss of slurry. After vibration and the resulting densification of the concrete mix has occurred, the sealing components may be depressurized and the various components of the apparatus can be separated in accordance with standard pipe forming techniques.
The objects and advantages of the present invention will be better understood upon a reading of the following specification in conjunction with the accompanying drawings, wherein: